1. Field of the Invention
The present invention relates to an idling rotation speed control apparatus for controlling, when an internal combustion engine is idled, the rotation speed of the engine mounted on a ship or a boat.
2. Description of the Related Art
With regard to an electronically controlled engine, as disclosed, for example, in Japanese Patent Publication No. 1995-33797, an idling rotation speed control method has been proposed in which the amount of air supplied to the engine in an idling state is controlled so that the rotation speed of the engine is controlled to be a predetermined value. However, it is necessary for a small boat such as a motorboat or a fishing boat to perform a trolling cruise in which the boat cruises at a constant speed that is within a low-speed range close to an idling state; therefore, in general, it is necessary for a waterman to perform a minute throttle operation. In some cases, pitching or rolling (or both) of a boat makes it difficult to perform a minute throttle operation; accordingly, for example, Japanese Patent Laid-Open No. 1999-218046 has proposed a control device in which an external resistor is made to perform a function of adjusting the rotation speed of the engine during a trolling cruise so that the amount of air is controlled only during a trolling cruise.
In general, an idling rotation speed control apparatus for an engine performs data setting to make the amount of air match a load on the engine so that the engine is steadily driven at a target rotation speed, and controls the idling rotation speed by performing direct feedback of a supply air amount, based on the difference between the target rotation speed and an actual rotation speed.
The desired value of the idling rotation speed of an outboard engine changes depending on whether the shift-lever position is the neutral, forward, or backward position, as well as depending on the engine temperature. Additionally, in a trolling cruise characteristic of a boat or a ship, a waterman is required to maintain, through his operation, the engine rotation speed to be within a rotation-speed range of 600 to 1500 turns, when the shift-lever position is at the forward position; therefore, in general, the engine is driven through throttle lever operation by a waterman. Because a boat engine is utilized in such a trolling cruise as described above, the load imposed on the engine in an idling state largely changes and the target rotation speed differs, depending on a driving condition; therefore, in order to control the rotation speed by directly increasing or decreasing air amount data when the idling rotation speed of an outboard engine is controlled, the number of setting data pieces in an ECU (Electronic Control Unit) becomes large, and a great number of man-hours for matching are required.
Additionally, in the case where, when an idling control apparatus is developed, a setting change, in an ignition timing or the like, that leads to a change in the engine-torque output characteristics occurs, it is necessary to implement matching again, because the amount of air necessary for making the engine steadily operate at a target rotation speed changes. Additionally, also in the case where the rotation speed is controlled by feeding back an air amount in accordance with the difference between the target rotation speed and an actual rotation speed, the control program becomes extremely complicated, because setting of the feedback gain differs depending on the target rotation speed or the load imposed on the engine when the engine operates. Additionally, in the case where a specification such as an engine capacity differs, massive data is required for each engine.
As described above, in the case where a high-accuracy idling rotation speed control apparatus for an outboard engine is configured, massive man-hours are required and matching data cannot universally be utilized; therefore, setting has been required for each engine. Additionally, in order to lighten the boat-handling load imposed on a waterman during a trolling cruise, it is required that, while the trolling cruise is performed through an idling rotation speed control apparatus, the trolling rotation speed can more readily and accurately be set even though the setting is performed even on board a ship that is rolling and pitching.